Typically, in the field of bicycles, the expression “right crank arm assembly” is used to indicate an assembly comprising a right crank arm and at least one toothed crown, or gear, coupled to the right crank arm. The toothed crown, in particular, is the toothed wheel configured to pull the chain of the bicycle for motion transmission to the rear wheel of the bicycle, such motion being imparted by the cyclist through pedaling.
Nowadays there is frequent use of right crank arm assemblies that comprise more than one toothed crown. In the field of racing bicycles there are typically two toothed crowns and they have different diameters.
In conventional bicycles, the right crank arm is directly coupled to the toothed crown having the greater diameter at respective surfaces defined on respective front faces of such components. In particular, referring to the inner side of the crank arm and of the toothed crown as the side intended, during use, to face towards the frame of the bicycle and to the outer side as the side opposite the inner side and intended, in use, to face towards the outside, the coupling between right crank arm and toothed crown having the greater diameter typically takes place at the inner side of the crank arm and at the outer side of the toothed crown having the greater diameter.
The toothed crown having the greater diameter has a diameter that is considerably greater than the toothed crown having a smaller diameter. In order to facilitate gear shifting from the toothed crown having a smaller diameter to the one having a greater diameter it is common to provide the inner face of the toothed crown having the greater diameter with a plurality of axially projecting elements, hereafter also referred to as “pins.”
The Applicant observed that the bicycle chain, in some operating conditions (especially in the so-called “maximum crossover” condition, i.e. when the chain engages the toothed crown having the smaller diameter—arranged axially closer to the frame of the bicycle—and at the rear wheel the sprocket having the smaller diameter—arranged axially farthest from the frame of the bicycle), touches the pins of the larger toothed crown and produces an annoying noise.
The Applicant also observed that such a noise is particularly accentuated in the case in which the right crank arm is made from composite material (for example carbon fibre) and is solid (i.e. without openings). In this case, the right crank arm behaves substantially like a “sound box”, actually amplifying the aforementioned noise.
It is an object of the present invention to provide a right crank arm assembly for a bicycle that allows a drastic reduction of the aforementioned noise in operation.